1. Technical Field
The present invention relates to a gain equalizer and a loss compensation method for compensating a deviation of loss among a plurality of optical signals each including a different wavelength in a wavelength multiplexed optical signal, an optical amplifier provided with the gain equalizer, and an optical amplification method using the gain equalizer.
2. Background Art
A wavelength division multiplex (WDM) communication system is well-known in optical communication systems. In the WDM communication system, a plurality of optical signals each having a different wavelength is multiplexed and transmitted. For the WDM communication system, several kinds of optical components, for example, a dispersion compensating fiber (DCF) for dispersion compensation, a gain equalizer and an optical amplifier are often used. Here, the gain equalizer is used for compensation a variation of gain among optical signals generated by amplification in the optical amplifier.
In a related art 1 (Published Japanese translation of PCT application No. 2002-506226 bulletin), an optical device with an arrayed-waveguide grating (AWG) for dispersion compensation is described. The optical device includes the AWG formed by the DCF, and an input line and an output line which are arranged for each waveguide. In the related art 1, the input line is connected to the output line so that the plurality of waveguides of the AWG is connected to each other in series, and optical signals pass through the plurality of waveguides. Therefore, dispersion generated in the optical signals is compensated.
A gain equalizer with one input port and one outputting port is described in a related art 2 (Japanese Patent Application Laid-Open No. 2005-49458). The gain equalizer is set a prescribed equivalent characteristic, and flattens the variation of gain among amplified optical signals by giving a loss corresponding to the equivalent characteristic to the optical signals.
Moreover, one of the technologies that relates to this invention is described in a related art 3 (US2008/0094692A1). The related art 3 describes a technology of a variable optical attenuator for keeping intensity of optical signals output from an optical amplifier constant, however, the related art 3 doesn't describe a technology of a gain equalizer for compensation a variation of intensity thereamong.